Chapter 16: The Molecular Basis of Inheritance
Teaching Objectives
DNA as the Genetic Material
1. Explain why researchers originally thought protein was the genetic material.
2. Summarize the experiments performed by the following scientists that provided evidence that DNA is the genetic material:
a.Frederick Griffith
b.Oswald Avery, Maclyn McCarty, and Colin MacLeod
c.Alfred Hershey and Martha Chase
d.Erwin Chargaff
3.Explain how Watson and Crick deduced the structure of DNA and describe the evidence they used. Explain the significance of the research of Rosalind Franklin.
- Describe the structure of DNA. Explain the base-pairing rule and describe its significance.
DNA Replication and Repair
5.Describe the semiconservative model of replication and the significance of the experiments of Matthew Meselson and Franklin Stahl.
6.Describe the process of DNA replication, including the role of the origins of replication and replication forks.
7.Explain the role of DNA polymerases in replication.
8.Explain what energy source drives the polymerization of DNA.
9.Define antiparallel and explain why continuous synthesis of both DNA strands is not possible.
10.Distinguish between the leading strand and the lagging strand.
11.Explain how the lagging strand is synthesized even though DNA polymerase can add nucleotides only to the 39 end. Describe the significance of Okazaki fragments.
12.Explain the roles of DNA ligase, primer, primase, helicase, topoisomerase, and single-strand binding proteins.
13.Explain why an analogy can be made comparing DNA replication to a locomotive made of DNA polymerase moving along a railroad track of DNA.
14.Explain the roles of DNA polymerase, mismatch repair enzymes, and nuclease in DNA proofreading and repair.
15.Describe the structure and function of telomeres.
16.Explain the possible significance of telomerase in germ cells and cancerous cells.
Student Misconceptions
1.The process of DNA replication is complex and difficult for students to master. Students must learn the details and understand the significance of many important processes: They must distinguish between 5’ 3’ and 3’ 5’ strands, understand the different mechanisms of replication for leading and lagging strands, learn the functions of a great variety of enzymes, and understand the energetics of the whole process. Students may master the many details of DNA replication but fail to understand their significance. It is important to emphasize why as well as how in teaching students about this fascinating and important topic.
2.Students may imagine separate DNA polymerase molecules moving along a stationary DNA molecule during the process of replication. It is important to point out that the polymerase enzymes involved in replication form a large protein complex, and that interactions between proteins in this complex greatly facilitate the efficiency of the replication process.
Key Terms
DNA ligase
DNA polymerase
double helix
helicase
lagging strand
leading strand
mismatch repair
nuclease
nucleotide excision repair
Okazaki fragment
origin of replication
phage
primase
primer
replication fork
semiconservative model
single-strand binding protein
telomerase
telomere
topoisomerase
transformation
Word Roots
helic- 5 a spiral (helicase: an enzyme that untwists the double helix of DNA at the replication forks)
liga- 5 bound or tied (DNA ligase: a linking enzyme for DNA replication)
-phage 5 to eat (bacteriophages: viruses that infect bacteria)
semi- 5 half (semiconservative model: type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand)
telos- 5 an end (telomere: the protective structure at each end of a eukaryotic chromosome)
trans- 5 across (transformation: a phenomenon in which external DNA is assimilated by a cell bacteriophage